1. Field of the Invention
The present invention relates to a rectangular and sheet-like cell, and particularly to the structure of a rectangular and sheet-like cell of high capacity type or integration type and its fabrication method.
2. Related Background Art
With the advancement of the electronics, there have been spread headphone stereos, compact disk players, compact cameras, video cameras, book-type personal computers, which involve the use of primary or secondary cells. Most of the cells employed are of cylindrical type. Cylindrical cells have a large dead space which is an unused portion within a cell box for accommodation, and recently, rectangular cells with less dead space to permit the effective use of the space have appeared. However, in the state of the art, cylindrical cells of spirally wound structure are able to have a larger plate area to supply a larger current flow, and have a higher energy density to attain superior performance, as compared with rectangular cells. Further, spirally wound cylindrical cells are easier to manufacture than rectangular cells. Therefore, there is a need for developing rectangular cells which are capable of supplying a large current flow, have a high energy density, and are easy to manufacture.
FIG. 10 is a schematic view of a spirally wound cylindrical cell, shown partly in cross section. FIG. 11A is a schematic view of a rectangular cell housed within a cell case, and FIG. 11B is a schematic constitutional view of a conventional rectangular cell. In FIG. 10, 901 is a positive electrode sheet made of positive electrode active material, 902 is a collector lead, 903 is a negative electrode sheet made of negative electrode active material. Reference numeral 904 is a collector, 905 is a separator holding an electrolyte, 906 is a cell case (negative electrode can), 907 is a positive electrode cap, 908 is an insulating gasket, 909 is an insulating plate, and 910 is an insulator or separator. This spirally wound cylindrical cell is constituted by packing the positive electrode sheet 901, the separator 905 and the negative electrode sheet 903, in a sandwiched and wound structure, within the cell case 906, connecting thereto a lead extended from the collector, adding an electrolyte thereto, and putting the positive electrode cap 907 thereon. In FIGS. 11A and 11B, 1001 is a positive plate made of positive electrode active material, 1002 is a collector, 1003 is a negative plate made of negative electrode active material, 1004 is a collector, 1005 is a separator holding an electrolyte, 1006 is a cell case (negative electrode can), 1007 is a positive electrode terminal, 1008 is an insulating gasket, 1009 is a cap, and 1010 is a collector lead. Within the rectangular cell, the positive plate 1001 and the negative plate 1003 are laminated with the separator 1005 therebetween, as shown in FIG. 11B.
From an external shape of the cell as shown in FIG. 10 and FIG. 11A, it can be seen that the rectangular cell will occupy only a slightly smaller dead space when accommodated within the device than that of the spirally wound cylindrical cell. However, from the comparison between the structures of FIG. 10 and FIGS. 11A and 11B, it can be seen that the spirally wound cylindrical cell can have a larger plate area, and a greater bulk density per volume of cell main body than the rectangular cell. Therefore, the conventional rectangular cell can have only a smaller plate area than the spirally wound cylindrical cell, and thus is difficult to pass as high a current flow as the spirally wound cylindrical cell, resulting in a substantial low energy density. Also, in the manufacturing process, the rectangular cell has a problem that it is involved in more manufacturing processes, and more complicated than the spirally wound cylindrical cell, because the rectangular cell involves the lamination of a plurality of positive and negative plates and the connection of a plurality of collector leads while the spirally wound cylindrical cell is made by the continuous lamination of positive electrode and negative electrode.